Video display systems generally display an image in an array of pixels. Among various video display systems, an optical projection system is known in the art to be capable of providing a high quality video display in a large scale. In one particular optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N actuated mirrors, wherein each of the M.times.N mirrors is coupled with each of the M.times.N actuators. The actuators are made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electrical signal applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as projection lens, thereby offering a displayed image thereon.
The present invention concerns primarily with a method for fabricating and mounting an array of M.times.N mirrors on an array of M.times.N electrodisplacive actuators to thereby form an array of M.times.N electrodisplacive actuated mirrors for use in the optical projection system described above.
In FIGS. 1A to 1F, there is illustrated a conventional fabrication processing sequence for fabricating an array of mirrors on an array of actuators. It involves, first, as shown in FIG. 1A, the formation of a separation layer 112 on a flat top surface of a substrate 110. The formation of the separation layer 112 is carried out by the spin-coating of a photoresist. Then, a first metallic layer 114 is deposited on top of the separation layer 112 by using, e.g., sputtering. The first metallic layer 114 serves as a reflector for reflecting incident light beams and is made of a light reflecting metal such as aluminum (Al). Subsequently, a second and a third metallic layers 116, 118 are applied on the first metallic layer 114 by using a similar technique used in the formation of the first metallic layer 114. The second metallic layer 116 functions as an intermediate layer for conferring good adhesion between the first metallic layer 114 and the third metallic layer 118. Copper (Cu) and nickel(Ni) are commonly used for the second layer 116 and the third metallic layer 118, respectively.
In the subsequent step, the metallic layers 114, 116, 118 are patterned into an M.times.N mirror array structure 120 by employing a conventional photolithography process, as shown in FIG. 1B. In the following step as shown in FIG. 1C, a photoresist layer 130, composed of the same photoresist as used in the separation layer 112, is applied onto the structure treated in the steps shown in FIGS. 1A to 1B, and subsequently defined for exposing the top surface of the third metallic layer 118. The exposed surface acts as a seed in the following electroplating process.
Thereafter, a fourth metallic layer 140, composed of the same metallic material as the one used in the forming of the third metallic layer 118, is electroplated, as shown in FIG. 1D, on the surface of the third metallic layer 118 which is not covered by the photoresist layer 130. An M.times.N actuator array 150 is then bonded onto a top surface of the fourth metallic layer 140 such that each of the actuators, e.g., 152, in the M.times.N actuator array 150 is aligned with each of the M.times.N mirrors in the M.times.N mirror array structure as shown in FIG. 1E, wherein each of the M.times.N mirrors is comprised of the metallic layers 114, 116, 118 and 140.
The photoresist layer 130 is then removed with the separation layer 112 concurrently to thereby disengage the substrate 110; and the formation of the M.times.N mirror array 160 is finalized as shown in FIG. 1F. The fourth metallic layer 140 works as a supporting layer for preventing the first metallic layer 114, which has a substantially larger surface area than that of the actuator, from sagging; and, therefore, the formation of the fourth metallic layer 140 is carried out by such an electroplating technique that can provide a sufficient thickness to suit the intended purpose.
In the above-described fabrication process for an M.times.N mirror array 160, as illustrated in FIGS. 1A to 1F, it involves the formation of multiple metallic layers, including a cumbersome electroplating process; and therefore, the processing steps tend to be complicated and costly.